1. Field of Invention
This invention pertains to modems used for digital data exchanges and more particularly to a subrate preamble decoder for decoding information prior to channel equalization acquisition.
2. Background of the Invention
Frequently modems are used to exchange data over different channels with equalizing means which are adaptive components for the signal distortion characteristics of each of the channels. At the beginning of each data exchange the remote modem may send a preamble which contains useful information. This preamble would precede the synchronization sequence used to set up the required equalizer parameters for the current data channel being used. Inherently, the preamble decoders required presetting of the equalizer and special circuits (and techniques) had to be used to find timing edges and levels which then enabled the decoder to properly decode the preamble signal.